Semiconductor memory device having faulty cells

ABSTRACT

In response to a read command received by a system interface unit for accessing a plurality of blocks of data stored in said non-volatile semiconductor memory, a controller carries out selective read operations of blocks of data to two memories from the non-volatile semiconductor memory. The controller also carries out parallel operations of data transferring a first block of data, which has already been subjected to error detection and error correction operations by an error correction unit, from one of the two memories to a host system via said system interface unit and of data transferring of a second block of data to be subjected to the error detection and error correction operation, from said non-volatile semiconductor memory to the other of the two memories.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation application of Ser. No. 11/931,881, filed Oct.31, 2007 (now U.S. Pat. No. 7,616,485), which, in turn, is acontinuation application of Ser. No. 10/629,808, filed Jul. 30, 2003(now abandoned), which, in turn, is a continuation of Ser. No.10/373,872, filed Feb. 27, 2003 (now U.S. Pat. No. 6,728,138), which, inturn, is a continuation of application Ser. No. 10/105,275, filed Mar.26, 2002 (now U.S. Pat. No. 6,542,405), which, in turn, is acontinuation of Ser. No. 09/886,133, filed Jun. 22, 2001 (now U.S. Pat.No. 6,388,920), which, in turn, is a continuation of application Ser.No. 09/824,778, filed Apr. 4, 2001 (now U.S. Pat. No. 6,317,371), which,in turn, is a continuation of application Ser. No. 09/477,665, filed onJan. 5, 2000 (now U.S. Pat. No. 6,236,601), which, in turn, is acontinuation of application Ser. No. 09/125,547, filed on Dec. 23, 1998(now U.S. Pat. No. 6,031,758), which is an application filed under 35USC §371 of International Application PCT/JP96/03501, filed Nov. 29,1996, and the entire disclosures of all of which are hereby incorporatedby reference.

TECHNICAL FIELD

The present invention relates in general to a semiconductor memorydevice in which an electrically reloadable nonvolatile semiconductormemory is used as a storage medium, and more particularly to asemiconductor memory device employing a semiconductor memory whichincludes partially faulty cells and which becomes faulty if thereloadable operation is carried out at frequent intervals.

BACKGROUND ART

An electrically reloadable nonvolatile memory has more advantageousfeatures as a memory device of an information apparatus in terms of thelow power consumption, the resistance against the vibrational shock, thehigh speed operation and the like as compared with other devices such asa magnetic memory device and an optical disc device. On the other hand,however, since the manufacturing process thereof is complicated and inaddition thereto, the operations which are in principle irreversibleagainst semiconductor are repeatedly carried out, there arises a problemthat occurrence of faulty portions and degradation in use thereof areremarkable. As a result, the manufacturing yield thereof is poor, thecost required therefore is expensive and reliability in operationthereof becomes a problem.

In order to solve the above-mentioned problems, the technique has beendeveloped such that the faulty portions of the memory are previouslyregistrated so as not to be used, and the number of times of use of thedata blocks is recorded and then if this number of times is increased,then the region of interest is replaced with another region to suppressthe increase in the number of times of use thereof, thereby increasingthe life of the semiconductor memory device. This technique is disclosedin JP-A-6-124596 for example.

According to this disclosed technique, there is provided a memory forstoring therein an address conversion table showing the comparisonbetween the logical addresses and the physical addresses, i.e., thecorrespondence between the logical address specified by a host and thecorresponding physical address on the memory. As a result, the physicaladdress of the faulty region is registered in the address conversiontable so as to show that it is faulty so that the logical addressspecified by the host is not assigned thereto, thereby preventing thefaulty portion from being used.

In addition, the number of times of erasing is administrated. That is,if the number of times of erasing has reached a fixed value, then thedata of the region of interest is replaced with the data of anotherregion and at the same time, the address values on the addressconversion table are reloaded to register again the data relating to thecorrespondence between the logical addresses and the physical addressesso that the proper correspondence therebetween can be obtained. All ofthe logical address values in use are registered in the above-mentionedaddress conversion table. Then, the high speed volatile memory such-as aDRAM or an SRAM is used as the storage-medium for the address conversiontable.

The reason of employing the high speed volatile memory is that theaddress conversion can be carried out at a high speed; when thereplacement of the address of interest with another address occurs, theregistration can be partially reloaded at a high speed; the mass storageof the data can be realized by utilizing the relatively inexpensivememory; and so forth.

In the above-mentioned prior art, since the registration of the addressconversion is carried out with respect to all of the logical addresses,when the memory device becomes of mass storage, the scale of the addressconversion table becomes large and hence the mass storage memory forregistration is required. In addition, since the memory device is of avolatile type, if the power source is disconnected, then all of the datastored therein will be erased. As a result, when turning on the powersource again, all of the registered values need to be written theretofrom another nonvolatile memory and hence the time period required forthe activation of the memory device is increased. This is a problem.

In addition, since the external memory for registration becomes of massstorage, there arises a problem that the number of components isincreased, which disturbs the miniaturization and the promotion oflowering the cost of the memory device.

In addition, if the nonvolatile memory is employed as theabove-mentioned memory for registration, then there arises a problemthat since the access time of the nonvolatile memory is generally long,the access time of the memory device itself becomes necessarily long.

In addition, if the back-up power source is provided for the volatilememory for registration, then the number of components is furtherincreased, which disturbs the miniaturization and the promotion oflowering the cost of the memory device. This is a problem.

In the light of the foregoing, it is therefore an object of the presentinvention to provide a mass storage semiconductor memory device, inwhich the miniaturization thereof and the promotion of lowering the costthereof can be made, and also the activation time and the access timeare reduced, by solving the above-mentioned problems associated with theprior art.

It is a concrete object of the present invention to provide, by eitherreducing the capacity of the external memory for registration orremoving the external memory for registration, a mass storagesemiconductor memory device in which the activation time and the accesstime are both short.

It is a concrete object of the present invention to provide, for use ina mass storage semiconductor memory device in which either the capacityof the external memory for registration is reduced or the externalmemory for registration is removed, an access method by which both ofthe activation time and the access time can be made short.

It is another object of the present invention to provide, for use in amass storage semiconductor memory device in which either the capacity ofthe external memory for registration is reduced or the external memoryfor registration is removed, a controller which is capable of realizingthe short activation time and access time.

DISCLOSURE OF INVENTION

According to the present invention, there is provided a semiconductormemory device in which a semiconductor memory having partially faultymemory cells each of which is defective in the function for storing datais used as a storage medium, and the holding of the data or the readingof the data thus held is carried out in blocks containing a plurality ofdata, the semiconductor memory device including: faulty locationregistering means for registering address values of faulty regionscontaining therein the memory cells each of which is defective in thestorage function in either ascending order or descending order dependingon the magnitudes of the address values in blocks; alternative storageregions as storage regions with the address values of which the addressvalues of the faulty regions are replaced in blocks; alternativelocation registering means for registering the replaced address valueswhich are obtained by replacing the address values of the faulty regionsstored in the faulty location registering means with the address valuesof the alternative regions; fault registration retrieval means forretrieving the faulty location registering means in order to judgewhether or not the address value in the region in or from which the datais held or read out corresponds to the address value on the faultyregion; access control means for carrying out the control so as, whenthe address value in the region in or from which the data is held orread out is registered in the faulty location registering means, toaccess the alternative region by referring to the alternative locationregistering means; and registration update means for carrying out, whena fault newly occurs, the reloading in accordance with the rule ofeither the ascending order or descending order in the faulty locationregistering means, the decision of the alternative location therefor andthe update of the alternative location registering means.

In addition, the fault registration retrieval means of the faultylocation registering means of the semiconductor device firstly devicesthe regions of the faulty location registering means into halves toestimate in which side the faulty location is present, and then dividesthe side of the halves in which the faulty location is estimated to bepresent into halves to estimate in which side the faulty location ispresent. By continuing this process, it is finally judged by the faultregistration retrieval means whether or not the data relating to thefaulty location is registered in the faulty location registering meansto carry out the retrieval thereof, thereby realizing the high speedretrieval.

In addition, according to the present invention, there is provided asemiconductor memory device in which a semiconductor memory havingpartially faulty memory cells each of which is defective in the functionof storing data is used as a storage medium, and when holding the dataor reading out the data thus held, a fixed amount of data which iscontinuously transferred is administrated as the data administrativeunit, and administrative information storage regions in whichadministrative information is stored every data administrative unit areprovided in the inside of the semiconductor memory, and which includesuse frequency administrating means for monitoring the use frequency ofthe data administrative unit, the semiconductor memory device includingadministrative information storage regions used to administrate aplurality of memory cells as an administrative storage unit and usefrequency administrating means for monitoring the use frequency ofblocks, wherein administrative addresses as the logical addresses whichare determined for the sake of convenience for administration areregistered in the administrative information storage regions of all ofthe blocks, and the administrative address of interest is made anaddress matching the physical address which is basically the physicaladdress value of the semiconductor memory so that in the access to thedata which is stored in the block specified by the administrativeaddress of interest, the physical address equal to the administrativeaddress of interest is accessed to carry out the desired access, whilewhen it is judged by the use frequency administrating means that thedata stored in the block should be exchanged for the data stored inanother block which is different in the use frequency therefrom, thedata stored in the block of interest is exchanged for the data stored inanother block, and during this exchange, the administrative address ofthe stored data is registered in the administrative information storageregion, and in the access to the data stored in subsequent blockspecified by the administrative address of interest, by referring to theadministrative address which is registered in the administrativeinformation storage region of the physical address equal to theadministrative address of interest, the physical address equal to theadministrative address value thus registered is accessed to obtain thedesired data stored in the associated block.

Then, when it is judged by the use frequency administrating means thatthe data of the block in which the above-mentioned administrativeaddress does not match the above-mentioned physical address due to thefact that the replacement of the data is already carried out needs to befurther replaced with the data of another block, after the compatibilityof the stored data with the administrative storage unit which became anobject when the replacement was carried out at the last time has beenreleased by carrying out the replacement again, the data stored in theregion of interest is replaced with the data stored in another region.

In addition, as another means, alternative address registration regionsfor the overall storage regions of the data, and alternation regions areprovided in the inside of the semiconductor memory. The alternativeaddress registration regions are arranged in the registration order inaccordance with the physical order for the storage of the data on thememory so that in the retrieval of the alternative addresses, theregistered location becomes uniquely clear on the basis of the physicalposition of the region to which the alternative was made.

Then, an administrative information region is provided every dataadministrative unit. At least the address information of the storeddata, the specific code exhibiting that the region of interest is notfaulty, and the error correction code for such administrativeinformation are stored in the administrative information region. Whenthe access request is issued from the outside, the error detection andcorrection of the corresponding region based on the error correctioncode, and the comparison with respect to the specific code exhibitingthat the region of interest is not faulty are carried out. Then, whenboth are normal, the region of interest is judged to be the usableregion to execute the access processing, while when one of them is notnormal, the region of interest is processed as the disusable region.

In addition, the storage regions in which the data of the dataadministrative units is temporarily stored are provided for two units.Then, the transfer of the data to/from the outside and the transfer ofthe data to/from the above-mentioned semiconductor memory are carriedout alternately, thereby making both the transfer possible at the sametime. In addition thereto, the control for carrying out the access withthe faulty memory cell avoided is processed in parallel to the transferof the data to/from the outside.

Since any of the address values of the regions which are not faulty isnot registered and only the address value of the region which is faultyis registered, the amount of registered data can be reduced and hencethe capacity of the memory for registration can be reduced. In addition,since the faulty addresses are registered in either ascending order ordescending order, when retrieving a certain address value, if anarbitrary location within the registration memory is referred, it can bedecided rashly whether the certain address value is registered on theside of the address values each smaller than the referred address valueor on the side of the address values each larger than the referredaddress value. From a large amount of registered values as well, it canbe judged at a relatively high speed whether or not the certain addressvalue is registered or in which location the certain address value isregistered.

In addition, in the case where the region in which the administrativeinformation is stored is provided in each of the blocks of the memory ofthe storage medium, the logical address value can be registered in thatregion, and also when the physical location of interest needs to bereplaced with another physical location due to the frequent reloadingand the like thereof, the logical address value within theadministrative information is replaced, thereby being able to copesimply with such a situation. In addition thereto, since those logicaladdress values do not need to be registered in the form of a table inthe external memory, there is no need of providing any other volatilememory, and also there is no need of reconstructing the table whenturning on the power source.

Then, when in the registration of those logical address values, for theblock for which the replacement was carried out one time, the additionalreplacement is required, the last replacement is returned to theoriginal state and then the required replacement is carried out, wherebythe number of times of reference, to the administrative informationregion, for grasping the logical address values has only to be one atthe most and hence the situation in which the reference is forced to bemade rotationally can be avoided.

In addition, according to the measure that if the fault registrationregion for all of the addresses is provided as another means, even ifthe access should be made to the faulty location, since from thatphysical location, the location where the alternative address isregistered can be uniquely determined, it is possible to shorten greatlythe retrieval time. In addition, since the judgment for the fault iscarried out on the basis of the two codes, i.e., the error correctioncode and the specific code exhibiting the region which is not faulty, itis possible to reduce remarkably the probability that the judgment withrespect to the fault/nonfault is made by mistake.

In addition, the storage regions in which the transfer data istemporarily stored are provided for two units, and in this connection,one is used in the transfer of the data to/from the outside, while theother is used in the transfer of the data to/from the memory, and thosetransfers are switched alternately over to each other, which results inboth of the transfers being able to be carried out at the same time. Inaddition thereto, in the case where the speed of the transfer of thedata to/from the memory is higher than the speed of the transfer of thedata to/from the outside, since the overhead time required for thejudgment whether or not the accessed region is faulty and the retrievalof the alternative address can lapse in the background of the transferof the data to/from the outside, the apparent transfer performance canbe improved.

In addition, according to the present invention, there is provided asemiconductor memory device in which a semiconductor memory havingpartially faulty cells is used for a part of or all of a storage medium,and when writing, holding or reading out the data to, in or from thestorage medium, a fixed amount of data is treated as a dataadministrative unit, the semiconductor memory including, in the insidethereof, storage regions in which the data of the data administrativeunit is stored, alternative regions of the storage regions and addressregistration regions of the alternative regions, wherein address valuesshowing the respective alternative regions are stored in addresses,within the regions in which the alternative addresses are registered, inaccordance with the address values in the storage regions.

In addition, the present invention may provide the semiconductor memorydevice wherein the storage regions include administrative information,respectively, and store therein, as the administration information,fault judgment information based on which it is judged whether or noteach of the storage regions is faulty, and when the access request ismade to the storage region of interest, it is judged whether or not thestorage region of interest thus accessed thereto is the usable regionusing the fault judgment information of the storage region of interest,and if it is judged that the storage region of interest is the usableregion, then the access processing is executed, while if it is judgedthat the storage region of interest is not the usable region, then thealternative address registration region is accessed to obtain thedesired address, and then the alternative region is accessed.

In addition, according to the present invention, there is provided asemiconductor memory device in which a semiconductor memory havingpartially faulty cells is used for a part of or all of a storage medium,and when writing, holding or reading out the data to, in or from thestorage medium, a fixed amount of data is treated as a dataadministrative unit, the semiconductor memory including, in the insidethereof, storage regions in which the data of the data administrativeunit is stored, alternative regions of the storage regions and addressregistration regions of the alternative regions, wherein the storageregions include administrative information, respectively, and storetherein, as the administrative information, fault judgment informationconsisting of correction information based on which the detection andcorrection of an error of the data stored in the storage regions arecarried out and detection information based on which it is detectedwhether or not each of the storage regions is faulty, and when theaccess request is made to the storage region of interest, it is judgedusing the fault judgment information corresponding to the storage regionof interest whether or not the storage region of interest thus accessedthereto is the usable region, and if it is judged that the storageregion of interest is the usable region, then the access processing isexecuted.

In addition, the present invention may provide the semiconductor memorydevice wherein the data which is different from the alternative addressvalue is registered in the registration location of the region which isnot faulty in the alternative address registration regions, so that itcan be judged whether or not the faulty region is registered.

In addition, the present invention may provide that with respect to thedifferent data, the bits thereof are either all 1s or all 0s.

In addition, the present invention may provide the semiconductor memorydevice wherein when the access request is made to the storage region ofinterest, the detection and correction of an error are carried out usingthe correction information, and when the discorrectable error isdetected, the storage region of interest is judged to be the disusableregion, while there is no error or when the correctable error iscorrected, it is detected using the detection information whether or notthe region of interest is faulty, and if it is judged that the region ofinterest is not faulty, then the region of interest is judged to be theusable region to execute the access processing, while if it is judgedthat the region of interest is faulty, then the region of interest isprocessed as the disusable region.

In addition, according to the present invention, there is provided asemiconductor memory device in which a semiconductor memory havingpartially faulty cells is used for a part of or all of a storage medium,and when writing, holding or reading out the data to, in or from thestorage medium, a fixed amount of data is treated as a dataadministrative unit, the semiconductor memory device including means forproducing and adding fault judgment information based on which for thetransfer data resulting from the request of storing data, it is judgedwhether or not a storage region in which the transfer data has beenstored becomes faulty after completion of the storage, wherein whenissuing the request of reading out the data thus stored, the faultjudgment processing is executed using the fault judgment information,and the storage region which has been judged to be faulty is treated asthe faulty region, and also the data which is stored in the faultyregion is transferred to the alternative region after having beencorrected.

In addition, the present invention may provide that the storage regionsin which the stored data of the data administrative unit is temporarilystored are provided for two units and outside the storage medium, andthe access processing using the fault judgment information is executedin parallel with the transfer of the data to/from the outside.

In addition, according to the present invention, there is provided amethod of accessing to a semiconductor memory device in which asemiconductor memory having partially faulty cells is used for a part ofor all of a storage medium, wherein the storage region which is providedin the inside of the semiconductor memory and in which the data isstored is accessed to judge whether or not it is faulty, and if it isjudged that the storage region of interest is not faulty, then thisaccess is continued, while if it is judged that the storage region ofinterest is faulty, then an address registration region of analternative region is accessed to obtain the address of the alternativeregion, and the alternative region is accessed on the basis of theaddress thus obtained.

In addition, according to the present invention, there is provided asemiconductor memory device in which a semiconductor memory havingpartially faulty cells is used for a part of or all of a storage medium,the semiconductor memory device including, in the inside thereof,storage regions in which the data of the data administrative unit isstored, alternative regions of the storage regions, and addressregistration regions of the alternative regions, wherein when accessingto the data stored in the semiconductor memory, a time period requiredfor accessing to the semiconductor memory in the case where thealternative region is not yet substituted for the data storage region isshorter than a time period required for accessing to the semiconductormemory in the case where the alternative region is already substitutedfor the data storage region.

In addition, according to the present invention, there is provided asemiconductor memory device in which a semiconductor memory havingpartially faulty cells is used for a part of or all of a storage medium,the semiconductor memory device including, in the inside thereof,storage regions in which the data of the data administrative unit isstored, alternative regions of the storage regions, and addressregistration regions of the alternative regions, wherein when accessingto the data stored in the semiconductor memory, the number of times ofaccess to the semiconductor memory in the case where the alternativeregion is not yet substituted for the data storage region is smallerthan the number of times of access to the semiconductor memory in thecase where the alternative region is already substituted for the datastorage region.

In addition, according to the present invention, there is provided asemiconductor memory controller for controlling writing and reading ofdata to and from a semiconductor memory storage medium having partiallyfaulty cells and including storage regions in which the data of dataadministrative unit is registered, alternative regions of the storageregions, and address registration regions of the alternative regions,wherein when there is issued a request of accessing to the storageregion of interest, using fault judgment information of the storageregion of interest exhibiting whether or not the data stored in thestorage region of interest is faulty, it is judged whether or not thestorage region of interest is a usable region, and if it is judged thatthe storage region of interest is a usable region, then the accessprocessing is executed.

In addition, the present invention may provide that when there is issuedthe request of accessing to the storage region of interest, usingcorrection information of the storage region of interest for the datastored in the storage region of interest, the error detection andcorrection are carried out, and when the discorrectable error has beendetected, the storage region of interest is judged to be the disusableregion, while when no error has been detected or when the correctableerror has been corrected, using detection information of the storageregion of interest based on which it is detected whether or not thestorage region of interest is faulty, it is detected whether or not thestorage region of interest is faulty, and if it is judged that thestorage region of interest is not faulty, then the storage region ofinterest is judged to be the usable region to execute the accessprocessing, while if it is judged that the storage region of interest isfaulty, then the storage region of interest is processed as thedisusable region.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram showing the overall configuration of a semiconductormemory device according to a first embodiment of the present invention;

FIG. 2 is a diagram showing a memory map of a storage medium;

FIGS. 3( a) and 3(b) are diagrams useful in explaining blockreplacement;

FIG. 4 is a flow chart showing the processing of retrieving an addressin response to an access request;

FIG. 5 is a flow chart showing the processing of replacing an addresswith another address;

FIG. 6 is a diagram showing the overall configuration of a semiconductormemory device according to a second embodiment of the present invention;

FIG. 7 is a diagram showing an example of data stored in anadministrative information region;

FIG. 8 is a flow chart showing the processing of determining an accesslocation;

FIG. 9 is a diagram showing a memory address map containing therein afaulty registration region; and

FIG. 10 is a flow chart showing the processing of judging whether or notan accessed block is faulty.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of the present invention will hereinafter bedescribed with reference to the accompanying drawings.

FIG. 1 is a diagram showing the overall configuration of the presentinvention. In the figure, reference numeral 1 designates an electricallyreloadable nonvolatile memory chip as a storage medium of asemiconductor memory device. In this connection, a flash memory isconsidered to be a memory which is most suitable for the electricallyreloadable nonvolatile memory chip 1. With respect to this memory chip1, it is assumed that the faulty regions are included therein in theratio having a determined upper limit. In addition, it is assumed thatthe data which is stored in the memory chip 1 is divided into blockseach having a plurality of data as a unit in order to be administrated,and an administrative information region is provided every block.

As for the storage capacities of the block and the administrativeinformation region, in the case of 32 Mbits (4 Mbytes) flash memory chipmanufactured by HITACHI, LTD., for example, one block is 512 bytes and16 bytes administrative information region is provided every block.Therefore, in one chip, 8,192 blocks are present and also the storagecapacity of 128 Kbytes is provided for the administrative informationregion. Such a flash memory can be taken as one example of the mostsuitable memory for the memory chip 1. But, it should be noted that thetotal storage capacity, the number of bytes of one block, and the amountof data of the administrative information region are not limited to theabove-mentioned values.

Reference numeral 2 designates a control circuit of the semiconductormemory device for coping with the access request issued from theoutside, or carrying out an access to the memory chip 1 and carrying outthe processings and the control within the device such as theadministration of the faulty regions and the number of times ofreloading. Reference numeral 3 designates a memory device forregistering the faulty regions. In this connection, since the memorydevice 3 is reloadable and makes possible a high speed access, a DRAM oran SRAM is most suitable for the memory device 3. But, a ROM which iselectrically reloadable in bytes can also be employed as the memorydevice 3 though it takes a lot of time for reloading and is relativelyexpensive. In the case of the ROM, its facility becomes as better as thedata does not need to be loaded thereinto when turning on the powersource.

Reference numeral 4 designates the semiconductor memory device of thepresent invention. Reference numeral 5 designates a system-bus throughwhich the access request is made to the present semiconductor memorydevice 4. In general, this system bus 5 is the peripheral bus of aninformation apparatus such as a personal computer. Reference numerals 6and 7 show an example of the stored data in the fault registrationmemory 3, i.e., reference numeral 6 designates address values as thefaulty regions, and reference numeral 7 designates replacement addressvalues with which the address values of the faulty regions are to bereplaced. As apparent from the figure, the adjacent address valuescorrespond to each other. For example, it is shown that the region ofthe faulty region address 8H is replaced with the region of thereplacement address 0H, in which the symbol “H” stands for hexadecimal.Incidentally, it is assumed in the present example that theregistrations of the faulty region addresses are arranged in ascendingorder.

The operation in the diagram of the present configuration willhereinbelow be described. The access request issued from the informationapparatus connected to the system bus 5 is transmitted to the controlcircuit 2 through the system bus 5. Then, the control circuit 2 decodesthe contents of the access request transmitted thereto to calculate theaddress of the data which has been transmitted thereto together with theaccess request. Then, the control circuit 2 recognizes the address valuethus obtained as the administrative address.

Next, the control circuit 2 divides the regions, of the faultregistration memory 3, to which the fault registration was made intohalves to judge in which side of the halves the administrative addressof interest is stored. For example, if the number of fault registrationsis 1,024, then the control circuit 2 accesses first to the 512-thregistered address. At this time, if that registered address is smallerthan the administrative address of interest which is previouslyobtained, then there is the possibility that the administrative addressof interest is stored in the region therebelow. On the other hand, ifthat registered address is larger than the administrative address ofinterest, then there is the possibility that the administrative addressof interest is stored in the region thereabove. Next, the controlcircuit 2 further divides the regions on the side in which there is thepossibility that the administrative address of interest is stored intohalves to judge in which side the administrative address of interest maybe registered.

Likewise, the control circuit 2 reads out either 256-th or 768-thregistered address to compare the registered address thus read out withthe administrative address of interest. In such a way, the amount ofdata to be compared is reduced half by half. Finally, it is judgedwhether or not the administrative address of interest is registeredtherein. If registered therein, then the corresponding replacementaddress value is obtained. Of course, in the case where when reducingthe amount of registered data half by half, the control circuit 2encounters the data equal to the administrative address of interest, thecontrol circuit 2 stops the retrieval at that time point.

In general, in the case where 1,024 registered data for example isretrieved in order to obtain the administrative data of interest, whensimply retrieving 1,024 registered data, the retrieval is required 1,024times at maximum and also the retrieval is required 512 times inaverage. However, according to the present method, by carrying out theretrieval 9 times at maximum, it is possible to find out surelyexistence and non-existence of the administrative data of interest andthe location thereof. If the administrative address value is notregistered, since the data of this administrative address value does notcorrespond to any of the faulty regions, it can be accessed as the dataof the normal block. If the fault registration is made for theadministrative address value of interest, the region of the replacementaddress value is accessed so that the desired access can be carried out.Incidentally, if for the replacement region, the last region in the datastorage regions is used, then the access thereto can be readily carriedout.

FIG. 2 shows the map of the storage regions which is used in this case.In the figure, reference numeral 11 designates total storage regionswhich include all of normal storage regions, faulty blocks and thereplacement regions. Reference numeral 12 designates normal data regionsconsisting of normal blocks and faulty blocks. Reference numeral 13designates replacement regions which occupy the lowest regions of thetotal storage regions. Reference numeral 14 designates the faulty blockX located within the normal data regions. Reference numeral 15designates a faulty block X located within the replacement regions. Asapparent from the figure, it is shown that the faulty block locatedwithin the normal data regions is replaced with the block which is notthe faulty block which is located within the replacement regions so asto correspond thereto.

Further giving the description with respect to the practical example, inthe case where by employing 32 Mbits flash memory manufactured byHITACHI, LTD. which is previously taken as an example, 20-chipssemiconductor memory device is constructed, the number of blocks is163,840. Since the address value thereof is 18 bits, the fault addressregistration requires 18 bits every registration. On the other hand,assuming that the upper limit of the number of faulty regions is 5% ofthe overall regions, 8,192 faulty blocks will be present at maximum.This can be represented with 14 bits.

As a result, one fault registration requires the data of 32 bits intotal of the faulty address values and the replacement address values,and hence the memory with 256 Kbits capacity is required for 8,192blocks. Currently, however, the memory with capacity of this degree isvery cheep. In this example, the total storage capacity of the normaldata regions is 163,840−8, 192=155,648 blocks. But, in the case wherethe fault registration memory is the nonvolatile memory, in order tostore the faulty registered data in the nonvolatile memory, theadditional 64 blocks are further used.

FIGS. 3( a) and 3(b) are diagrams useful in explaining a method of usingthe administrative information regions within the nonvolatile memory 1.In the figures, reference numeral 21 designates the data storagecontents of the nonvolatile memory as the storage medium of thesemiconductor memory device of the present invention which contents areshown in the form of a diagram, reference numeral 22 designates astorage block of a physical address 1 (the number of the physicaladdress is assumed to start with 1) of the nonvolatile memory, andreference numeral 23 designates a block of a physical address 2. In thisconnection, this block 23 is assumed to be the faulty block. Referencenumeral 24 designates a block of a physical address 4 and referencenumeral 25 designates a block of a physical address 7.

Reference numeral 30 designates data of an administrative address 1which is stored in the block of the physical address 1, referencenumeral 31 designates data of an administrative address 7 which isstored in the block of the physical address 4, and reference numeral 32designates data of an administrative address 4 which is stored in theblock of the physical address 7. That is, in the figure, the data of theadministrative address 4 and the data of the administrative address 7are replaced with each other. This reason is that since the data of theadministrative address 7 is the data having the property such that thereloading is carried out frequently, the progress of degradation of theblock of the physical address 7 needs to be suppressed. For this reason,the data of the physical address 7 is replaced with the data of thephysical address 4.

Reference numerals 26, 27, 28 and 29 designate respectively theadministrative information regions corresponding to the respectiveblocks of the physical addresses. In the administrative informationregions 26, 27, 28 and 29, the administrative addresses of the datawhich are stored in the respective blocks are registered. The controlcircuit 2 of the present semiconductor memory device accesses, whenrequiring an access to the administrative address 1, to theadministrative information region 26 of the physical address 1 and whenthe administrative address value registered therein is 1, accesses tothe data of the corresponding block, thereby enabling the desired accessto be carried out. It is understood that if the administrative address 4is accessed in the state shown in this example, then the administrativeinformation region 28 of the physical address 4 is accessed and on thebasis of the administrative address value 7 registered therein, thephysical address 7 is accessed so that the access to the desiredadministrative address 4 can be carried out.

Now, in the case where next to this state, it is judged that withrespect to the block as well of the physical address 4, the progress ofthe degradation thereof should be suppressed due to the further frequentreloading which is made to the administrative address 7, first of all,the data of the administrative address 4 is transferred to the physicaladdress 4 to be returned back to the original address, and next it isreplaced with the data of the block which becomes an object ofreplacement. In the present example, the administrative address 1 isselected as that object of replacement. The state after completion ofthe replacement is shown in FIG. 3( b).

If this replacement work is not carried out, then the three-sidedreplacement will occur among the administrative addresses 1, 4 and 7. Asa result, for example, if the administrative address 1 is intended to beaccessed, first of all, the administrative information region 26 of thephysical address 1 is accessed to obtain the administrative address 7,and next, the administrative information region 29 of the physicaladdress 7 is accessed to obtain the administrative address value 4 sothat the desired access can be carried out. If the replacement isfurther continued to occur, then the rotation of the access to theadministrative information regions occurs in order to carry out thedesired access and as a result, the access processing performance willbe remarkably reduced.

FIGS. 4 and 5 show flow charts each useful in explaining the operationof the semiconductor memory device of the present invention. FIG. 4 is aflow chart useful in explaining the grasping of the physical addresswhich is used to know where the data of the address corresponding to theaccess request is physically stored when issuing the access request(Step 401). First of all, the capacity of the faulty addressregistration memory is divided into halves (Step 402). For example, inthe case of the memory with 64 Kbytes capacity, the capacity of thismemory is divided into halves each having 32 bytes capacity.

Next, the leading address on the lower side is accessed (Step 403). Inthe case of the memory with 64 Kbytes capacity, the address value atthis time is 8000H. Then, the data which is obtained when accessing tothe leading address on the memory (i.e., bits of the stored data, andthe number thereof depends on the total number of fault registrationaddresses) is compared with the address corresponding to the accessrequest (Step 404). Then, if that data is larger than the requestaddress, then there is the possibility that the request address maypresent on one side of the halves in which the smaller addresses arestored. On the other hand, if that data is smaller than the requestaddress, then there is the possibility that the request address maypresent on the other side of the halves in which the larger addressesare stored.

This reason is because the address values located within the faultregistration memory are arranged in either ascending order or descendingorder. In this connection, at this time, the two address values maymatch each other. In this case, since it becomes clear that the addressvalue of interest is faultily registered, the alternative addressthereof is read out (Step 405) and then it is regarded as the physicaladdress to be obtained (Step 406) and the physical address is obtained(Step 415). Next, it is judged whether or not the regions on the side inwhich the data of interest is estimated to be present are dividable(Steps 407, 409). If dividable, they are equally divided into halves(Steps 408, 410). Then, likewise, the data of interest is compared withthe address corresponding to the access request (Step 404) to estimateon which side the request address is present.

While after on which side of the halves the request address is presenthas been able to be estimated, the regions corresponding to the side ofinterest are further divided into halves, finally, the region can not bedivided into halves any more. In the case where even when the divisionbecomes impossible, the data of interest does not match the requestaddress, the request address is judged to be the address which is notfaultily registered. Then, the administrative region of the physicaladdress of interest is accessed to obtain the administrative address(Step 411). If the physical address matches the administrative address(Step 412), then the region of interest corresponds to the region towhich the access request was made (Step 413). On the other hand, ifmatching is not obtained, then the region of the physical address whichis equal to the obtained administrative address value corresponds to theregion to which the access request was made (Step 414).

The processing shown in this flow chart is executed in the writeoperation as well as in the read operation. In the read operation, thephysical address which has been obtained through this processing, andthe access processing is completed after sending the data. On the otherhand, in the write operation, the processing shown in FIG. 5 is furtherrequired. First of all, when the write operation is requested (Step501), physical address (1) is obtained from object logical address (1)(Step 502). The data which is stored in the obtained physical address(1) becomes unnecessary to be erased since the new data is alreadypresent (Step 503).

At this time, it is checked whether or not there is necessity of theaddress replacement due to the frequent reloading of the physicaladdress (1) of interest (Step 505). As for an example of this method,the data relating to the number of times of reloading is recorded, andif the data has reached the fixed number of times (Step 504), then it isjudged that there is necessity of replacement. On the other hand, whenit is judged that there is no need of the replacement, if the given datais directly written to the physical address (1) (Step 506), then theaccess will be completed (Step 507).

On the other hand, if it is judged that there is need of carrying outthe replacement, then the physical address (2) as an object of thereplacement is selected (Step 508). As for an example of a selectionmethod, it is considered that the record of the number of times ofreloading a little while ago is retrieved and then the region of theless number of times of reloading is selected. After completion of theselection, next, the administrative address value (1) of the physicaladdress (1) which was an object of the writing is compared with thephysical address (1) (Step 509). If the physical address value (1)matches the administrative address value (1), then it is judged that thesector of interest is not the sector in the state in which thereplacement has been carried out. Therefore, if the data which is storedin the physical address (2) as an object of the replacement is directlywritten to the physical address (1) the data of which is already erased,and the data of the physical address (2) is erased and then the data ofthe administrative address (1) is written thereto (Step 510), then theaccess operation is completed (Step 507).

On the other hand, if the physical address value (1) does not match theadministrative address value (1), then it is judged that the region ofinterest is the region in which the replacement is being carried out.Therefore, first of all, that replacement must be cancelled. Since theadministrative address value(1) exhibits the physical address value (3)which is an object of the replacement, the data stored therein istransferred to the physical address (1) the data of which is alreadyerased, thereby cancelling the replacement (Step 511).

Next, the data of the physical address (3) is erased, and then the dataof the physical address (2) which is a new object of the replacement iswritten thereto (Step 512). Finally, the data of the physical address(2) is erased and then the data of the new administrative address (1)thus obtained is written to the physical address (2) (step 513), therebycompleting the write operation (Step 507). The foregoing is theprocessing during the write operation.

The explanation of the operation of the embodiment of the semiconductormemory device according to the present invention has been completed.According to the present embodiment, there is provided the effect thatit is possible to realize readily the semiconductor memory device whichis interchangeable with any of the existing magnetic disc storagedevices.

Next, another embodiment of the present invention will hereinafter bedescribed with reference to FIGS. 6 to 10. In these figures, partssimilar to those previously described are denoted by the same referencenumerals.

FIG. 6 is a diagram showing a configuration of a flash memory card towhich the present invention is applied. In FIG. 6, reference numeral 50designates the above-mentioned flash memory card, reference numeral 51designates a controller to which the present invention is applied, andreference numeral 52 designates an electrically reloadable nonvolatilememory as a storage medium (hereinafter, referred to as “a memory” forshort, when applicable). The inside of the memory 52 is divided everyregion having a predetermined size (hereinafter, referred to as “ablock” for short in the present embodiment), and each block consists ofa storage data region 53 in which the storage data sent from the host isstored, and an administrative information region 54 in which theadministrative information used to administrate the storage data region53 is stored.

The storage data region 53 and the administrative information region 54are in all referred to as a block. While in the present embodiment, thedescription is given with respect to the specific case where the memorywhich has the storage data regions 53 each having 512 bytes capacity andthe administrative information regions 54 each having 16 bytes capacityis employed as the memory 52, it should be noted that the presentinvention is not limited thereto. Reference numeral 55 designates an ECC(Error Correcting Code) circuit for the storage data regions 53(hereinafter, referred to as “a data ECC” for short, when applicable)for producing an error correcting code for a part of or all of the datawithin each of the storage data regions 53, and detecting and correctingerrors, which are generated in transfer or storage, using the errorcorrecting code thus produced, and reference numeral 56 designates,likewise, an ECC circuit for the administration information regions 54(hereinafter, referred to as “an administrative ECC circuit” for short,when applicable). Incidentally, while the ECC may mean the code in whichthe correcting object data itself is contained therein in some cases, inthe present embodiment, it is treated separately from the correctingobject data.

Reference numeral 57 designates an I/F control circuit fortransmitting/receiving, in response to the access from the host (notshown) such as a personal computer, the data to/from the host throughthe system bus 5. By the system bus 5 is meant the standard interfacesuch as a PC Card Standard, or an AT Attachment Interface. Referencenumeral 58 designates a data transfer control circuit for controllingthe data transfer among the host, the memory 52, the data ECC circuit55/administrative ECC circuit 56, and buffers as will be describedlater.

Reference numeral 59 designates a buffer for data for holdingtemporarily therein the data when transferring the stored data 53, andreference numeral 60 designates, likewise, a buffer for theadministrative information region 54. In this connection, a set ofbuffers 59 and 60, A, and a set of buffers 59 and 60, B, are provided.Reference numeral 61 designates a host side buffer switching circuit forswitching the two sets of buffers 59 and 60, reference numeral 62designates, likewise, a memory side buffer switching circuit, andreference numeral 63 designates a CPU for controlling all of thoseelements.

FIG. 7 is a diagram showing an example of the contents of theadministrative information region 54. In the figure, reference numeral66 designates an error correcting code for the stored data (hereinafter,referred to as “an ECC for data” for short, when applicable), stored inthe storage data region 53, which ECC for data is produced by the dataECC circuit 55, reference numeral 67 designates a storage block codewhich is used to record the kind of data stored in the storage dataregion 53 corresponding to the present administrative information region54, e.g., identification codes each exhibiting the identification withrespect to the constitutive information data, the data of the driveinformation, the data of the normal file, and the like, and to recordthe replacement addresses which are used to average the degradation, andreference numeral 68 designates a degradation record in which the degreeof degradation of the block of interest is recorded in the form of adetermined numeric value. For example, the number of times of erasing ofthe block of interest is suitable for the degradation record 68.

Reference numeral 69 designates an nonfaulty block code which is used tocheck predetermined codes, which are stored in the blocks, respectively,when reading out these codes, thereby identifying whether or not thesecodes are faulty, and reference numeral 70 designates an errorcorrecting code for the administrative information regions 54(hereinafter, referred to as “an ECC for administration” for short, whenapplicable). But, the ECC for administration 70 does not need tocorrespond to all of the data within the administrative informationregions 54. For example, since the ECC for data 66 itself is an objectof the error correction, it does not need to be made an object of theECC for administration 70. In addition, the nonfaulty block code 69 ispreferably excellent in the error detection capability and may not havethe correction capability. In this example, each administrativeinformation region 54 has a capacity of 16 bytes.

Next, the description will hereinbelow be given with respect to theoutline of the operation of the flash memory card having a configurationshown in FIG. 6.

First of all, the host (not shown) transfers both of a write command andwrite data to the specified address through the system bus 5. In thepresent embodiment, it is assumed that the flash memory card 50 isinterchangeable with the hard disc and hence it is also assumed that thewrite operation can be instructed on the basis of the cylinder, thehead, the sector number and the like similarly to the hard disc. Thedata transfer control circuit 58 stores temporarily the write data inthe data buffer 59. On reception of the write data, the CPU 63 analyzesboth of the write command and the setting value which is previously setby the host to carry out the address calculation and finds out thecorresponding block located within the memory 52 by the method as willbe described later.

In this connection, in the case where the memory for which the erasingprocessing is required is employed as the memory 52 in the presentembodiment, the erasing processing is executed.

Next, under the control by the CPU 63, the data transfer control circuit58 writes the stored data within the data buffer 59 to the storage dataregion 53 of the above-mentioned corresponding block. In addition, theECC for data 66 is produced by the data ECC circuit 55, and also thedegradation record 68 and the like within the administrative informationwhich has been read out from the administrative information region 54when finding out the write block are changed in accordance with the newstorage, so that the corresponding ECC for administration 70 is producedby the administrative ECC circuit 56. Then, the data transfer controlcircuit 58 stores the administrative information in the administrativeinformation region 54 of the same block on the heels of the operation ofwriting the stored data. Both of the stored data and the administrativeinformation are written collectively in the form of one block to thememory 52.

Incidentally, if the control is carried out in such a way that thestored data which has been sent from the host and the administrativeinformation which has been read out from the memory 52 are stored in thedifferent sets of buffers, respectively, using both of the host sidebuffer switching circuit 61 and the memory side buffer switching circuit62, then the time period required for that processing can be shorteneddue to the parallel processing.

When the host requests the operation of reading out the stored data,similarly to the storage operation, the CPU 63 and the data transfercontrol circuit 58 find out the corresponding block from the memory 52in accordance with the read command issued thereto, and read out thestored data from the memory 52 to store the stored data thus read out inthe buffer 59. Next, the error detection of the data of the storage dataregion 53 is carried out using the ECC for data 66. If it is judged thatthere is no error, then the data is directly transferred to the host. Onthe other hand, if the error is detected, then the data containing theerror thus detected is corrected to be transferred to the host. At thesame time, the CPU 63 treats the block of interest as the faulty blockto execute the alternative processing therefor. If the discorrectableerror is detected, then the fact that such an error has been detected isreported to the host.

When a plurality of blocks are accessed, the two sets of data buffers Aand B are alternately used to read out the data from the memory 52 andat the same time, to transfer the data to the host in paralleltherewith.

If the erasing is required when the host requests the writing of thedata, similarly to the foregoing, the corresponding block is found outand then the erasing of the data in the corresponding block is carriedout. During this processing, if the replacement is necessary as a resultof searching the degradation record 68, then the block as an object ofreplacement is selected using the well known method to read out thecontents thereof, the storage block code 67 is rewritten, and thecontents of the storage data region 53 and the contents of theadministrative information region 54 are replaced with each other exceptfor the degradation record 68. In the case where the erasing is carriedout, on the basis of a predetermined method, the degradation record 68is updated if necessary.

In addition, in the case where the speed of the transfer of the datafrom the memory 52 is higher than that of the transfer of the data tothe host, for a time period left over, with respect to the block towhich the next access will be made, the nonfault check and the retrievalof the alternative address as will be described later can be made usingthe two data buffers, which contributes to the promotion of high speedperformance.

Next, a method of retrieving the block in response to the access requestissued from the host, as the feature of the present invention, willhereinbelow be described in more detail with reference to FIGS. 8 and 9.

FIG. 8 is a flow chart useful in explaining the processing to the extentof computing, by the CPU, the physical address value on the memory 52 inresponse to the access command issued thereto when the access requesthas been issued from the host.

Normally, when intending to carry out the access, the host carries outthe access without being conscious of the data storage location on thememory. In the present embodiment, it is assumed that the memory cardmay be replaced with the hard disc, and hence as described above, thehost issues the access command similar to that in the hard disc.

The CPU 63 receives the above-mentioned command issued from the I/Fcontrol circuit 57 and calculates the logical address valuecorresponding to the arrangement of the data storage on the memory (Step801). Next, the CPU 63 accesses the corresponding address of the memory52 on the basis of the logical address value thus calculated (Step 802),and then reads out the administrative information stored in theadministrative information region 54. Incidentally, it is assumed thatin the inside of the memory 52, all of the contents of one block areread out to the buffer in the memory 52 in accordance with the address,and only either the administrative information or the stored data issent from that buffer to the controller 51. Then, it is judged on thebasis of the administrative information thus sent whether or not theblock of interest is a usable nonfaulty block (Step 803). This judgmentmethod will be described later with reference to FIG. 9.

Next, the processing of interest branches off in the followingprocessings depending on the judgment result. First of all, if it isjudged that the block of interest is the nonfaulty block (the block ofinterest may be corrected on the basis of the ECC), then the CPU 63obtains the storage block code 67 within the administrative informationregion 54 which has been read out to be written to the buffer 60 (Step804). Then, the replacement address value stored in the storage blockcode 67 is compared with the logical address value based on which thepresent block has been come to be accessed (Step 805). If matching isobtained, then the block of interest is the block in which thereplacement does not occur, and hence the block of interest is directlyjudged to be the access block to be accessed (Step 806). During the readaccess, the stored data is read out from the buffer within theabove-mentioned memory 52. During the write access, the administrativeinformation corresponding to the stored data which is already set in thebuffer 59 to be written thereto.

On the other hand, if the mismatching is obtained, then the replacementhas occurred and hence it can be judged that the block corresponding tothe replacement address value within the storage block code 67 is theaccess block. Therefore, the block of the physical address value whichthe storage block code 67 exhibits is newly accessed (Step 807). Whenaccessing to the block to which the replacement has been made, thenonfaulty block check may further be carried out.

On the other hand, if it is judged that the block of interest is thefaulty block, then the fault registration region as will be describedlater is newly accessed (Step 808). If the block of interest is alreadyregistered in the fault registration region (Step 809), then theregistrated value, i.e., the alternative address is obtained, and theblock of the corresponding physical address value is accessed (Step810).

On the other hand, if the fault registration is not yet made to thefault registration region, then it is judged that the block of interestis the faulty block which has newly occurred (Step 811), and hence theaccess to the block of interest is impossible. In the case of the readaccess, the CPU 63 informs the host of the access error. In the case ofthe write access, since the data is already rewritten, there is no needof informing the host of the error occurrence, and hence the alternativeblock is assigned thereto and the data is stored in the alternativeblock. At the same time, the CPU 63 writes the alternative block addressto the region corresponding to the faulty block located within the faultregistration region 84.

In the case where the above-mentioned faulty block information is notheld in the external memory but is held in the inside, if the faultyblock information is formerly searched, then the following problemsarise. That is, since the access time of the nonvolatile memory is long,it takes time to carry out the search. In addition, since the access ofthe flash memory is carried out in blocks, in order to obtain theindividual fault registration information, the fault registrationinformation will be collectively read out and also the sequential accesswill be made to the fault registration information. For this reason, ittakes time to access to somewhat the last of the information in thefault registration region.

The above-mentioned method was provided in order to solve the foregoingproblems. According to the above-mentioned method, first of all, thefault registration region is not searched, but the corresponding blockis accessed using the logical address. Then, the present invention mayprovide the method wherein the fault registration is not accessed tillit is judged that the block associated with the information obtainedfrom the administrative information region is faulty. Therefore, thenumber of times of access to the memory till the data stored in thenonfaulty block is obtained is reduced and hence the access time viewedfrom the host is shortened.

In addition, the present invention may provide the method wherein in thecase where the block of interest is not faulty, but for the purpose ofaveraging the number of times of reloading, the block is replaced withanother block, the access is carried out in accordance with the addressinformation within the storage block code 67.

In addition, the present invention may provide the method wherein in thecase where the block of interest in the memory 52 is faulty, since thereis no reliability in the information as well within the above-mentionedadministrative information region 54, the alternative block informationis not stored in the storage block code 67 or something like that, butis stored in the fault registration region which is separately provided.While in the access to the fault registration region, the sequentialaccess as described above exerts an influence thereon, since the faultoccurrence rate is low, there is no problem.

Next, the fault registration method as described above will hereinbelowbe described in more detail.

FIG. 9 shows an example of a memory map in the inside of the memory 52,and the contents which are registered in the storage data region 53 ofone block in the fault registration region. In the figure, referencenumeral 81 designates a memory map of the overall storage region or apart thereof, i.e., one chip or the like of the memory, referencenumeral 82 designates a general storage block group in which the data isstored in correspondence to the logical address values in the memory map81, reference numeral 83 designates an alternative block group in whichthe faulty block which is present or occurs in the general storage blockis replaced to store the data, and reference numeral 84 designates afault registration region in which the alternative address when havingcarried out the replacement is registered. In the fault registrationregion 84, the alternative address is registered in a part of thestorage data region 53.

In the fault registration region 84, the registration region for all ofthe blocks of the general storage block group 82 is ensured. Inaddition, the blocks of the general storage block group 82 are madecorrespond to the registration regions in the fault registration region84. While it is assumed in the present embodiment that the data isassigned to the fault registration region in the order of the addressesof the general storage block, it should be noted that the presentinvention is not limited thereto.

In the present embodiment, as shown in FIG. 9, for the faultregistration, 2 bytes are assigned to every block. In this connection,reference numeral 85 shows the case where the block of interest (itsaddress is 0000) of the general storage block 82 is not faulty, and asone example, FFFF are registered therein. While the value exhibitingthat the block of interest is not faulty may be the value which may notbe the alternative block address, in order to make simple the judgmentwhether or not the fault registration is made in Step 809 of FIG. 8 asdescribed above, it is preferable that all of the bits are made either1s or 0s. Reference numeral 86 shows that the block of the generalstorage block address 0003 is faultily registered, and it is replacedwith the block of the alternative block address 0003. In addition, it isshown in 86 that the general storage block addresses 0006 and 0007 arereplaced with the alternative block addresses 0004 and 0005,respectively.

Since the address assignment in the inside of the alternative blockgroup 83 sufficiently cover the alternative addresses, the registrationthereof is possible with the less number of bytes. Whether or not thefault registration is made can be judged depending on the judgmentwhether the registered value is FFFF or the address value other thanFFFF is registered as the registered value. Incidentally, it isdesirable that the ECC is produced in the fault registration region 84as well in order to improve the reliability. In this case, in the sameprocedure as that of the general storage block, the ECC circuit may beapplied thereto.

Next, the description will hereinbelow be given with respect to theprocessing of judging whether or not the accessed block is faulty.

FIG. 10 is a flow chart useful in explaining the judgment whether or notthe block of interest is faulty, and more particularly useful inexplaining in more detail the nonfaulty block check (Step 803) in theoverall flow chart shown in FIG. 8.

First of all, the CPU 63 accesses to the block of interest on the basisof the obtained logical address to read out the administrativeinformation within the administrative information region 54 (Step 1001).Then, using the ECC for administration 70 of the administrativeinformation thus read out, the CPU 63 detects the error of the obtainedadministrative information (Step 1002). Then, the processing branchesinto the three states, i.e., no error, detection of a correctable errorand detection of a discorrectable error. In the case of the detection ofthe discorrectable error, the block of interest is judged to be thefaulty block, and then the processing proceeds to the processing ofretrieving the fault registration region 84 (Step 808). On the otherhand, in the case of the detection of the correctable error, theprocessing of the correcting the error is executed (Step 1003). In thecase of no error or completion of the execution of the correction, thenonfaulty block code 69 which has been read out is checked (Step 1004).

As described above with reference to FIG. 7 as well, the nonfaulty blockcode 69 is used to confirm matching or mismatching on the basis of thespecific code which is previously stored and which is common to all ofthe blocks. If though no error is detected through the check by the ECCfor administration 70, matching is not obtained for the nonfaulty blockcode 69, then it is judged that the false detection has occurred. Inother words, this is the phenomenon which is caused when the code ofinterest due to the occurrence of the error accidentally matches thecode with no error.

In addition, in the case where though likewise, the error correctionprocessing is executed, the mismatching is obtained for the nonfaultyblock code 69, it is judged that the code of interest due to theoccurrence of the error accidentally matches the correctable code sothat the false correction is made, and on the basis of this judgment,the block of interest is regarded as the faulty block. Then, theprocessing proceeds to the processing of retrieving the faultregistration region 84. In the case other than the above-mentionedcases, the block of interest is judged to be the block with no error orthe nonfaulty block for which the correction is already made.

Incidentally, the case is also naturally conceivable where aftercompletion of the false detection or the false correction, matching isaccidentally obtained for the nonfaulty block code. However, theprobability of occurrence of the false detection or the false correctionitself is very low, and in addition thereto, it can be judged that theprobability in which matching is accidentally obtained for the nonfaultyblock code may not be actually caused. In addition, such judgment can becarried out employing the ECC method wherein the false detection rate orthe false correction rate is not large, and also by increasing thenumber of bits of the nonfaulty block code.

As set forth hereinabove, according to the present embodiments, thereare provided the following effects:

1. Since the information of the faulty blocks is registered in the faultregistration regions 84 located within the memory 52, no externalregistration memory is required.

2. Since the administrative information of the block corresponding tothe logical address is looked at in advance to judge whether or not theblock of interest is faulty, the number of times of access to the memory52 from the controller is effectively reduced as compared with themethod of searching the fault registration information in advance, andtherefore, the access time, up to a time point when obtaining theobjective data, viewed from the host side can be shortened.

Accordingly, the improvements in the processing speed and thereliability are possible in the judgment whether or not the block ofinterest is faulty, and the promotion of the high speed, the highperformance and the high reliability of the memory device itself can berealized. In addition, since no external memory is used, the promotionof the low cost can also be realized.

Incidentally, by integrating the controller 51 and the memory 52 of theabove-mentioned embodiments into one chip, there is obtained the effectthat the buffer in the memory 52, and the buffers 59 and 60 in thecontroller 51 can be collectively arranged so that the scale of thecircuitry can be reduced. In addition, since the signal linesdistributed between the controller 51 and the memory 52 becomesunnecessary, there is provided the effect that the package having theless number of terminals can be employed.

INDUSTRIAL APPLICABILITY

According to the present invention, in a semiconductor memory devicehaving partially faulty cells, the capacity of a memory can be reducedor deleted which is used in conversion address registration resultingfrom the replacement or substitution of addresses, and further theretrieval of fault can be carried out at a higher speed. Accordingly,both of the promotion of high speed of access and the promotion oflowering the cost thereof become possible.

In addition, even in the case where a nonvolatile memory is used inwhich there is a limitation in the number of times of reloading, andalso an address is replaced with another address, the address retrievalcan be made at a higher speed and hence it is possible to improve theaccess performance.

1. A nonvolatile memory apparatus comprising: a control unit; a main storage medium of the apparatus including a plurality of electrically reloadable nonvolatile memory devices each having a plurality of memory cells, wherein the electrically reloadable nonvolatile memory devices are adapted to be operable even when faulty memory cells exist therein; and a reloadable fault registration memory for registering address values of faulty regions of the main storage medium containing therein the faulty memory cells, wherein data which is stored in the electrically reloadable nonvolatile memory devices are divided into blocks, each block having a plurality of data to be administrated and which is assigned an access address by the control unit, an administrative information region being provided in each block, and wherein the control unit is adapted to carry out (i) access requests of the main storage medium and (ii) the administration of faulty regions and a number of reloading occurrences of reloading of respective ones of the memory cells of the electrically reloadable nonvolatile memory devices in the main storage medium.
 2. A nonvolatile memory apparatus comprising according to claim 1, wherein, when the control unit detects a faulty memory cell associated with a respective block, the control unit is adapted to enter an access address of that block including the faulty memory cell as a registered address value in the reloadable fault registration memory, and wherein, when the control unit receives an access request, the control unit decodes contents of the access request transmitted thereto to calculate an address of the data which has been transmitted thereto together with the access request and then recognizes an address value obtained as an administrative address, the control unit then ascertains from contents of the reloadable fault registration memory whether or not the access value is associated with a faulty memory cell in the main storage medium and if it is determined to be a faulty memory cell, a replacement address value with which the address value of the faulty memory cell is to be replaced is designated in the reloadable fault registration memory.
 3. A nonvolatile memory apparatus comprising according to claim 2, wherein the reloadable fault registration memory includes a dynamic random access memory (DRAM) or a static random access memory (SRAM).
 4. A nonvolatile memory apparatus comprising according to claim 1, wherein the reloadable fault registration memory includes a dynamic random access memory (DRAM) or a static random access memory (SRAM).
 5. A nonvolatile memory apparatus comprising according to claim 1, wherein the electrically reloadable nonvolatile memory contains a plurality of flash memory chips.
 6. A nonvolatile memory apparatus comprising according to claim 5, wherein the reloadable fault registration memory includes a dynamic random access memory (DRAM) or a static random access memory (SRAM). 